By optimizing the gain configuration and length of the loop, a 90-tone optical frequency comb (OFC) is successfully generated based on recirculating frequency shifter structure. The peak-to-peak power fluctuation of the 90-tone OFC is 4.26 dB and the tone-to-noise ratio is higher than 19.17 dB. To further analyze the noise accumulation feature of the tones when travelling around the loop, linewidth of the tones is measured by delayed self-heterodyne interferometer structure. The result shows the linewidth of the tones deteriorates little during the recirculating process, indicating that the generated OFC is an ideal multi-wavelength source for high-speed communication systems.

We report experiments of ultraviolet (UV) communication based on spread-spectrum technique. Field mea-surements via online UV communication are conducted to compare the system performances with and with-out spectrum spreading. The results indicate that the spread-spectrum technique is capable of suppressing noise in UV atmospheric scattering channel and therefore improve the system performance evidently. Details of implementation are also provided to make the results useful for similar system design in research on optical wireless communications.

We propose and experimentally demonstrate a 2 × 2 imaging multiple-input–multiple-output (MIMO) Nyquist single carrier visible light communication (VLC) system based on spectral efficient 64/32-ary quadrature amplitude modulation, as well as pre- and post-equalizations. Two commercially available red–green–blue light-emitting diodes (LEDs) with 3 dB bandwidth of 10 MHz and two avalanche photodiodes with 3 dB bandwidth of 100 MHz are employed. Due to the limited experiment condition, three different colors/wavelengths are transmitted separately. The achieved data rates of red, green, and blue LED chips are 1.5, 1.25, and 1.25 Gb/s, respectively. The resulting bit error ratios are below the 7% pre-forward error correction limit of 3.8 × 10-3 after 75 cm indoor transmission. To the best of our knowledge, this is the first experimental investigation of imaging MIMO system, and it is the highest data rate ever achieved in MIMO VLC system.

We present a high-speed visible light communication (VLC) link that uses a commercially available phosphorescent white light-emitting diode (LED). Such devices have few megahertz bandwidth due to the slow response of phosphorescent component, which severely limit the transmission data rate of VLC system. We propose a simple pre-emphasis circuit. With blue-filtering and the pre-emphasis circuit, the bandwidth of VLC system can be enhanced from 3 to 77.6 MHz, which allows non-return-to-zero on-off-keying (NRZ–OOK) data transmission up to 200 Mb/s with the bit error ratio of 5.3 × 10-7 which is below 10-6. The VLC link operates at the room illumination level of ~1000 lx at 1.1 m range using a single 1 W white LED.

We propose a joint scheme for symbol, sampling clock, and carrier frequency synchronization in a polarization division multiplexing coherent optical orthogonal frequency division multiplexing (PDM-CO-OFDM) system. Unlike other existing algorithms designed for specific impairment, the scheme can estimate and compensate for the interactional synchronization errors effectively without extra training overhead by building a compre-hensive error model. The simulation shows that symbol synchronization error and sample timing error can be corrected by channel equalizer, and the estimation ranges of sampling frequency offset and normalized carrier frequency offset are about (-2000, 2000)ppm, and (-0.04 (-3.5), 0.04 (3.5))Ghz, respectively.

A data-aided method of joint frequency offset and chromatic dispersion estimation based on the Chu training sequences is shown in 112 Gb/s polarization-multiplexed (PM) quadrature phase-shift keying and 224 Gb/s PM-16-quadrature amplitude modulation with different pulse-shaping filters, respectively. The proposed method achieves a good accuracy and is verified to be robust to polarization mode dispersion.

We show a simple, convenient, and cost-effective scheme for tunable frequency upconversion at millimeter-wave band without a local oscillator. By launching a 2.5-Gb/s directly modulated baseband signal into a Fabry–Pérot laser diode (FP-LD), the mode of the FP-LD is locked by the high-order sideband of the injected signal. The beating frequency of the injection-locked mode and the injected signal can generate upconversion subcarriers. In our experiment, tunable frequency subcarriers of 28.4, 29.3, and 30.5 GHz are obtained without any radio-frequency local oscillator. The single sideband phase noises of 83.88, 76.36, and 78.54 dBc/Hz @ 10 kHz (at 28.4-, 29.3-, and 30.5-GHz subcarriers, respectively) are shown. The proposed scheme has potential to generate much higher frequency carriers.

We present a particle filter (PF)-based algorithm to detect and track maneuvering infrared weak multiple targets at different signal-to-noise ratios for the scenes with the multiple targets number unknown and varying. A detecting filter and a tracking filter based on sequential likelihood ratio (LR) testing with fixed sample size are designed, respectively, for capturing new target and tracking confirmed targets. The algorithm is optimized with selectively particles sampling and adaptive process noise. Targets birth and death time are accurately estimated according to the change degree of the LR along with the corresponding state amended through PF backward recursion. Simulation results show that it is positive to detect and track maneuvering infrared weak multiple targets with the appearance and disappearance of more than one, which also achieves a significant improvement in state estimation especially for the time targets which appear and disappear.

A new photoacoustic (PA) signal sampling and image reconstruction method, called compressive sampling PA tomography (CSPAT), is recently proposed to make low sampling rate and high-resolution PA tomography possible. A key problem within the CSPAT framework is the design of optic masks. We propose to use edge expander codes-based masks instead of the conventional random distribution masks, and efficient total variation (TV) regularization-based model to formulate the associated problem. The edge expander codes-based masks, corresponding to non-uniform sampling schemes, are validated by both theoretical analysis and results from computer simulations. The proposed method is expected to enhance the capability of CSPAT for reducing the number of measurements and fast data acquisition.

We experimentally research linear polarization characteristics of various terrains at millimeter wave band for image interpretation. We measure and discuss the polarization phenomena, and consider as well the incident angle which also affects terrain radiometric temperature. An economic single-channel radiometer is used in measurements, and changes to the linear polarization are produced by manually rotating its waveguide. We demonstrate that the characteristic in polarization is a decisive advantage of terrain identification in ways beyond that which can be achieved using an intensity radiometer alone.

We experimentally evaluate and correct the non-equivalence between electrical and radiative heating of solar irradiance absolute radiometer to compensate the systematic error of radiant power measurement at ambient pressure. A relative difference of the order of 0.08%–0.27% between electrical and radiative heating sensitivities is shown, and the resulting non-equivalence correction factor is calculated. The radiant power measurement equation is modified using the non-equivalence correction factor, a systematic deviation of 0.19% of radiant power measurement is hence eliminated.

We propose a blind spot elimination method based on an improved layout of CCD in spacecraft jitter estimation. At least three CCDs are required and designed with two pairs of overlapping area and one non-overlap-ping pair. The two number of lines in space of overlapping pairs are made coprime to minimize the number of common blind spots. The third non-overlapping pair is arranged with the space less than the quotient of the least line frequency and bandwidth. It is used to eliminate the aliasing blind frequencies of the first two overlapping pairs. Experimental results prove the effectiveness of the blind band elimination.

We demonstrate a narrowband optical filter which operates on the 52S1/2 to 52P3/2 transition at 780 nm in rubidium vapor based on optical-pumping-induced dichroism combined with Faraday anomalous dispersion effects. Its peak transmission is 18.4(2)% at the 52S1/2, F = 2 to 52P3/2, F ' = 1, 3 crossover transition, whereas at the 52S1/2, F = 2 to 52P3/2, F ' = 2, 3 crossover transition the transmission is 18.6(2)%. Both transitions have a bandwidth (full-width at half-maximum of peak transmission) as narrow as 24.5(8) MHz, which is remarkably improved compared with the narrowest bandwidth as we know. This technique can also be applied to other alkali atoms.

We propose an approach for realizing 3D reconstruction in small field of view or some extreme environments. We combine the stereo vision and the structured light technologies and change the traditional ways of ap-plying them by employing two fiber bundles. The processes of calibration and 3D reconstruction are also introduced. Experiments are performed to verify the feasibility and effectiveness of our proposed approach.

An Nd:glass disc requires an edge cladding to absorb the amplified spontaneous emission. The absorption is determined by reflections (R) from disc edges. R is primarily induced by the refractive index (n) mismatch. Thus, the temperature at the cladding interface increases due to absorption, and leads to the variation of n. In order to investigate the effect of temperature on the refractive index match, temperature coefficients (dn/dT) of the laser glass, adhesive polymer, and cladding glass are measured. The effect of temperature on the refractive index match is discussed. Results show that the indices match below 40°C.

We propose and demonstrate a scheme to smooth and shape the on-target patterns in multimode fiber lasers, which includes expanding–collimating system and lens array (LA). A smooth pattern with flat-top and sharp-edge profiles can be obtained with the irradiation nonuniformity decreasing significantly. We analyze the effects of the parameters such as defocus distance, the tilt angles, the number of the incident fiber lasers, and the diffraction-weakened LA on the uniformity irradiation of target by numerical simulations.

We show that resonant tunneling of electromagnetic (EM) fields can occur through a six-layer structure con-sisting of two pairs of bilayer slabs: one being an epsilon-negative layer and the other being a mu-negative layer with a double-positive (DPS) medium and air. This type of tunneling is accompanied by high-magnetic field. The Poynting vector distributions and the material dissipation are studied. Our results demonstrate that the EM field in the structure is controlled flexibly by single-negative media and DPS slab. Therefore, this structure has potential applications in wireless energy transfer.

A series of Ca4.99(PO4)3F:1%Eu3+, 1%X (X = Li+, Au3+, and Bi3+) nanoparticles are prepared using hydro-thermal method, with an average size of 33–62 nm. We study the improved photoluminescence properties of Ca4.99(PO4)3F:1%Eu3+ by co-doping with Li+, Au3+, and Bi3+ ions, respectively, and the enhancement of the emission intensities of Eu3+ is observed in these samples. The effects of Li+ acting as a charge compensator, Au3+ as a plasma surface sensitizer, and Bi3+ as an energy conversion agent are discussed. The results show Ca4.99(PO4)3F:1%Eu3+, 1%X nanoparticles are a promising candidate as a red component for near-ultraviolet light-emitting diodes.

The emerging perfect-absorber metamaterials (PAMs) provide an alternative material approach for the next generation of electromagnetic detection at any frequency band of interest. One type of dual cross-shaped PAMs is developed to obtain multiplex-band spectrum absorption at mid-infrared region. Three distinct absorption peaks are attributed to the polarization sensitivity excitation of the plasmonic resonance. The charge density distributions, which are excited by resonant electromagnetic waves passing through the PAMs medium, provide insights into the observed absorption behavior. We find that the retrieved optical properties of the PAMs including permittivity and permeability are still consistent with the sum of the Drude and Lorentz type models at wavelengths ranging from 2.0 to 10.0 mm. Such multiplex-band absorption properties enable the proposed PAMs a powerful tool for the direct detection of multiple molecular vibrational structures, and for multiple spectra infrared detection.

Three kinds of KH2PO4 raw material are used to grow deuterated potassium dihydrogen phosphate (DKDP) crystals by traditional and rapid growth methods, respectively. The growth habit dependence on the purity of raw material is described and analyzed. The optical properties including transmission spectra and laser-induced damage threshold of these crystals have been measured. It is found that the growth method affects the optical properties of crystal more obviously than the raw material with the mass content of main metal ions below 1 ppm. Moreover, the morphology of the core in the observed damage sites indicates that an explosion process probably occurs during laser-induced breakdown.

We propose an ultra-wideband optical diode device based on two-dimensional square-lattice photonic crystals. For the device, the odd mode is completely transmitted in one direction and converted to the fundamental even mode, but completely reflected in the other direction. The operation bandwidth of the device is preserved within a rather wide range of frequencies, which is over 6.5% of the central frequency. A directional coupler and 90° bend are utilized as the composite function device with mode filter and mode converter. It is possible that the photonic crystal device can help to construct on-chip optical logical devices and benefit greatly to the optical systems with multiple spatial modes.

We fabricate white phosphorescent organic light-emitting diodes (PHOLEDs) with three dopants and double emissive layer (EML) to achieve color stability. The white PHOLEDs use FIrpic dopant for blue EML (B-EML), and Ir(ppy)3:Ir(piq)3 dopants for green:red EML (GR-EML) with N,N.'-dicarbazolyl-3, 5-benzene (mCP) as host material. Thicknesses of B-EML and GR-EML are adjusted to form a narrow recombination zone at two EML's interface and charge trapping happens in EML according to wide highest occupied molecular orbital and/or lowest unoccupied molecular orbital energy band gap of mCP and smaller energy band gap of dopants. The total thickness of both EMLs is fixed at 30 nm in the device structure of ITO (150 nm)/MoO3 (2 nm)/N,N'-diphenyl-N,N'-bis(l-naphthyl-phenyl)-(l,l'-biphenyl)-4, 4'-diamine (70?nm)/mCP:Firpic-8.0% (12?nm)/mCP:Ir(ppy)3-3.0%:Ir(piq)3-1.5% (18 nm)/2',2',2''-(1,3,5-benzinetriyl)-tris(1-phenyl-1-H-benzimidazole) (30 nm)/8-hydroxyquinolinolato-lithium (2 nm)/Al (120 nm). White PHOLED shows 18.25 cd/A of luminous efficiency and white color coordinates of (0.358 and 0.378) at 5000 cd/m2 and color stability with slight CIEXY change of (0.028 and 0.002) as increasing luminance from 1000 to 5000 cd/m2.

We investigate the propagation characteristics of the narrowband Stokes/anti-Stokes photons in cold atomic vapor. The four-wave mixing process results from parametric amplification of the anti-Stokes photons. We find that the process of parametric amplification is very similar to the light pulse propagating through an anomalous dispersion gain medium. Finally, we obtain the general solutions of the Glauber biphoton correlation functions, which are in good agreement with the experiment results.

High-strain InGaAs/GaAs quantum wells (QWs) are grown by low-pressure metal-organic chemical vapor deposition (LP-MOCVD). Photoluminescence (PL) at room temperature is applied for evaluation of the optical property. The influence of growth temperature, V/III ratio, and growth rate on PL characteristic are investigated. It is found that the growth temperature and V/III ratio have strong effects on the peak wavelength and PL intensity. The full-width at half-maximum (FWHM) of PL peak increases with higher growth rate of InGaAs layer. The FWHM of the PL peak located at 1039 nm is 20.1 meV, which grows at 600 °C with V/III ratio of 42.7 and growth rate of 0.96 mm/h.

In the quantum key distribution system, quantum channel is always affected by spontaneous Raman scattering noise when it transmits with classical channels that act as synchronization and data channels on a shared fiber. To study the effect of the noise exactly, the temporal distribution characteristics of the Raman scattering noise are analyzed theoretically and measured by a single-photon detector. On the basis of this, a scheme to decrease the noise is proposed.